Deployment of radio repeaters is a possible means to enhance the performance of radio network coverage. A radio repeater is typically provided with two antennas placed in different positions. An incoming signal is received on one of the antennas, amplified and transmitted (forwarded) on the other antenna. The repeater antennas are typically used differently in the uplink and downlink. The antenna used to receive the downlink signal is also used to transmit the amplified uplink signal and vice versa.
In TDD (Time Division Duplex) radio networks uplink and downlink transmission is time multiplexed on the same carrier frequency. Thus, a radio repeater in a TDD network should not amplify the uplink and downlink at the same time. Instead the radio repeater must somehow determine which direction (uplink or downlink) is currently active and operate accordingly. A scenario in which the time slot usage (uplink or downlink) changes over time and between cells is especially challenging.
US 2007/0015462 A1 describes a method addressing this conflict based on receiving and analyzing the TDD schedule transmitted to the mobiles also at the repeaters. By extracting the time periods used for downlink and uplink from this schedule, it is possible to separate amplification in the two directions in time. However, a drawback of this method is that the repeaters will amplify signals to and from all mobiles or users, regardless of whether this is actually necessary. Not only does this waste power for connections that do not require amplification, it also creates unnecessary interference.
Although radio repeaters in FDD (Frequency Division Duplex) can transmit simultaneously in both the uplink and downlink (since the two links occupy different frequency bands), they still have the same drawback as radio repeaters in a TDD system, namely that they will amplify signals to and from all mobiles or users, regardless of whether this is actually necessary.